The present invention relates to a television signal receiving apparatus and more particularly to a receiving apparatus of the type having a picture-in picture function which receives as an input a plurality of television signals subjected to a band width compressing process by multiple sub-Nyquist sampling.
According to the existing television standards, television receiving apparatus of the type having a so-called picture-in-picture function to simultaneously show pictures from a plurality of channels on one picture screen are known. An example thereof is disclosed for example in JP-A-49-2419 and receivers having this function have been put in practical use.
Presently, the receivers of this type have generally had a construction in which the necessary luminance signal and chrominance signals for the reproduction of color pictures are respectively converted to baseband signals and, after such processes as timebase compression have been effected, the sub-channel signals are inserted into the main channel side. For instance, as shown in FIG. 2, on the main channel side an NTSC first video signal, supplied to a first signal input terminal 1, is processed through a first luminance processing circuit 11 and a first chrominance signal demodulator 12 and these processing circuits respectively supply the resulting luminance signal and two color difference signals to one input terminal of the corresponding switches SW.sub.1 to SW.sub.3. On the subchannel side, the NTSC second video signal from a second signal input terminal 2 is processed through a second luminance processing circuit 21 and a second chrominance signal demodulator 22, and time compression circuits 23 and 24 respectively supply a subchannel side luminance signal and two color difference signals which were subjected to time base compression in synchronism with the phase of signals supplied from a main channel-side synchronizing circuit 13 through lead wires 25 to the other input terminal of the switches SW.sub.1 to SW.sub.3. A signal selecting circuit 15 including the switches SW.sub.1 to SW.sub.3 is switched by a control signal supplied from the synchronizing circuit 13 through a lead wire 14 so as to combine the main channel-side and subchannel-side signals in the same picture and thus three primary color signals R, G and B are respectively delivered to output terminals 17, 18 and 19 through a De-matrix circuit 16.
On the other hand, in accordance with a high quality television system, a method of effecting band width compression by multiple sub-Nyquist sampling for the transmission of its wide band video signals has been proposed see [The Institute of Television Engineers of Japan, Research Society Report "HD-TV Broadcasting System Using Single Channel Satellite (MUSE)", TEBS 95-2 Vol. 7, No. 44].
This MUSE system is designed so that an offset is provided in sampling phase between the fields, the frames and the lines and the processing is performed in such a manner that one cycle of the sampling phase is completed by four fields or two frames, thereby transmitting video signals. Thus, a receiving apparatus includes for example a frame memory to store video signals successively transmitted for four fields and then the signals are combined to restore a still picture portion and also a moving picture portion is restored by spatial interpolation within a single field. An example of a receiving apparatus according to the MUSE system will now be described with reference to FIG. 3.
A digitized picture signal is applied to a signal input terminal 300 and the signal is supplied through a lead wire 301 to an interframe interpolating circuit including a switch 302 and a frame memory 303. The switch 302 multiplexes an incoming input signal and the signal of the preceding frame fed back from the frame memory 303 to select and deliver the resulting picture signal subjected to interframe interpolation. On the other hand, the picture signal supplied to the signal input terminal 300 is also supplied through a lead wire 305 to a spatial interpolating circuit 306 which performs a given filtering process and the spatial interpolating circuit 306 supplies a signal for the moving portion in the picture to a mixer circuit 308 through a lead wire 307. The picture signal subjected to interframe interpolation and delivered onto the lead wire 304 is supplied to each of the mixer circuit 308 and a motion detecting circuit 311 through lead wires 309 and 310, respectively. The output of the frame memory 303 is supplied to the other input of the motion detecting circuit 311 through a lead wire 312 so that the moving portion is detected by using the frame correlation of the pictures and a motion control signal is supplied to the mixer circuit 308 through a lead wire 313.
Thus, in response to the motion control signal supplied through the lead wire 313, the mixer circuit 308 outputs the signal from the lead wire 309 with respect to the picture elements of the still picture portion and the signal from the lead wire 307 with respect to the picture elements of the moving picture portion by mixing them at a given ratio or selectively. The output of the mixer circuit 308 is supplied through a lead wire 316 to a field memory 314 and one input of an interpolating filter 315 for performing an interpolating process between fields, and the interpolating filter 315 is designed so that in response to the motion control signal supplied from the motion detecting circuit 311 through a lead wire 317, an interfield interpolating process is performed only on the picture elements of the still picture portion and a restored high quality television picture is delivered to a signal output terminal 316.
The above-described receiving apparatus according to the MUSE system is used for the purpose of restoring the original picture signal of the high quality television system from a band width compressed incoming signal. Thus, where the picture-in-picture operation is performed by such a receiving apparatus, it is conceivable to arrange receiving apparatus of the construction shown in FIG. 3 in parallel so that after restoring the mainchannel and sub-channel band width compressed high quality television signals, the signals are combined by such known method as shown in FIG. 2.
However, this construction has serious practical disadvantages in that the scale of the receiving apparatus for picture-in-picture operation is increased by more than two times and so on.